let cache = new Map()
cache.set('a',1)
cache.set('b',2)
cache.set('c',3)

// console.log(cache.keys().next().value)


for (let key of cache.keys()) {
  console.log(key) // a,b,c
}

for (let key of cache.values()) {
  console.log(key) // 1,2,3
}